This invention relates to apparatus for monitoring physiological variables, and more particularly relates to apparatus for producing audible and visible output responsive to changes in a physiological variable such as the temperature of a human fingertip.
Monitoring of physiolgical variables is important to researchers, doctors, physiologists, and persons who wish to learn to exercise control over processes which are mediated autonomically, hormonally, or reflexly. Such monitoring is indispensable to persons who wish to achieve muscular relaxation, said relaxation being inversely proportional to the activity of the sympathetic branch of the autonomic nervous system.
For example, the temperature of an extremity, such as a fingertip, is proportional to the rate of blood flow through the extremity. The autonomic nervous system controls the rate of blood flow (circulation) to all parts of the body including the extremities. Sympathetic stimulation reduces the blood flow to the extremities. Thus, fingertip temperature varies inversely with the activity of the sympathetic branch of the autonomic nervous system, and monitoring fingertip temperature and rendering it in visible or audible form reveals the state of activity of the sympathetic nervous system, as well as the related state of skeleto-muscular and smooth muscular relaxation.
Such relaxation reduces stress created ailments such as high blood pressure, tension, and headaches.
Existing devices for monitoring physiological variables have serious deficiencies. One such deficiency is the use of electrodes. These conductive elements are used to establish conductive electrical contact with the anatomical site being monitored. In contrast to electrodes, there exist `sensors` which do not require conductive electrical contact with the anatomical site being monitored.
The contact resistance between such an electrode and the anatomical site depends on the surface state of the electrode, the surface state of the anatomical site, the shapes of the electrode and the site, the pressure between electrode and site, and divers other factors. Sometimes conductive creams must be used to improve contact. The contact resistance is extremely variable and almost impossible to control or reproduce. Thus, even experienced professionals suffer great difficulties when using electrodes.
Another such deficiency is the use of either electrodes or sensors which are attached to the main apparatus by means of electrical cables. The cables are subject to tangling and breakage. The cable connectors frequently develop contact problems. The electrodes or sensors must be taped or fastened to the body. Further, while non-electrically contacting sensors do not depend on electrically conductive contact with the body, they do depend on reasonably consistent physical contact and this is hard to achieve through taping or tying. Also, the relatively unprotected sensors are easily damaged.
Yet other deficiencies include complex controls requiring operator training, complex output formats requiring professional interpretation, excessive power consumption and large size thus limiting portability and location of use, and high cost tending to limit ownership to a small group of professionals.
One attempt to overcome a few of these deficiencies is described in U.S. Pat. No. 3,648,686 (Payne--Mar. 14, 1972). Unfortunately, the Payne device still has a number of serious disadvantages. Firstly, it utilizes electrodes to sense galvanic ski response and therefore it is subject to all of the attendant ills of electrodes. Secondly, it lacks visual output. Thirdly, its audible output is a continuous tone, an output format which has been found to be fatiguing to the listener. Fourthly, galvanic skin response does not correlate as well with muscular relaxation as do other methods such as peripheral circulation thermography.
It has been discovered that all of these aforementioned deficiencies can be overcome by a radical approach which places a sensor, said sensor not depending on conductive electrical contact with the anatomical site being monitored, in the wall of a supporting surface wherein the shape of the supporting surface and the positional relationship of the sensor to the surface serve to establish the required positional relationship between the sensor and the anatomical site being monitored, and which combines these with an audible transducer, a visible transducer, a control, a novel electronic circuit, and a battery such that variation of a physiological variable of the anatomical site adjacent to the sensor and support surface causes variation of output from at least one of the transducers.
The electronic circuit includes a novel tone circuit and an interupter circuit. Power consumption is minimized through the use of complimentary-metal-oxide-semiconductor integrated circuits (CMOS) and through a unique series output circuit. A loud speaker and a light emitting diode supply audible and visible output. The control connects to the tone circuit and establishes an initial operating tone. An On-Off switch is linked to the control. Power is supplied by a nine volt battery, assuring safe operation.
The CMOS circuits are members of a family of circuits designated 74C and intended primarily for digital use. The present invention uses them for both digital and analog functions thus realizing very low power consumption and low cost.
Traditionally, a tone is made to vary in accordance with the parametric variations of a sensor by utilizing the snesor as one of the frequency determining components of an oscillator circuit. This method suffers from limited sensitivity. Greater sensitivity can be obtained through the use of a bridge followed by amplification. However, a bridge requires three additional stable components and an amplifier adds power consumption and cost.
It has been discovered that great sensitivity at low cost and low power consumption can be obtained through a novel configuration of an integrator and a Schmitt type trigger. This configuration is especially favorable in conjunction with CMOS circuitry. Further, such a configuration provides easy initial adjustability and can be arranged to provide for comparison monitoring between two like sensors.
It has further been discovered that a pleasing and effective output format can be realized by using an interupter to periodically start and stop an output tone and by combining a loudspeaker of falling low frequency amplitude with a filter capacitor and an acoustic baffle.
It is one object of the present invention to provide a monitor of physiological variables which utilizes an electrically non-contacting sensor rather than electrodes.
Another object is to provide a monitor of physiological variables with a supporting surface which automatically maintains proper contact between the sensor and the anatomical site being monitored.
Still another object is to provide a monitor of physiological variables which is portable by virtue of low weight, battery power, and low power consumption.
Yet another object is to provide a monitor of physiological variables which is suitable for consumer use by virtue of low cost, simple operation, and simple output format.
One more object is to provide a monitor which is highly suited to thermography.
Still another object is to provide a reliable easy-to-use apparatus to monitor sympathetic nervous system activity.
It is another object of the present invention to provide apparatus for rendering changes of physiological variables as variations of visible or audible output.
Yet another object is to provide apparatus for biofeedback training.
Yet another object is to provide apparatus for biofeedback training that senses a physiological variable which correlates highly with skeleto-muscular and smooth muscular relaxation.